Traditional wireless networks include a number of base stations (BTS) and one or more mobile switching centers (MSC)/base station controllers (BSC). The BTSs each cover a geographic region, or cell of the wireless network and communicate with mobile telephones in the cell. The MSCs/BSCs provide switch and soft handoff functionality for the wireless network. To support data calls, wireless networks typically include a data interworking function (IWF). The IWF connects the wireless network to the Internet or other data network.
Each cell of a wireless network is able to support a certain number of wireless calls. This capacity is a function of frequency reuse, carrier to interference ratio, bit-energy to noise ratio, effective bit-rate protocol and other criteria of the wireless link. The wireless link may be based on established standards such as IS-54 (TDMA), IS-95 (CDMA), GMS and AMPS, 802.11 based WLAN, new upcoming standards such as CDMA 2000 and W-CDMA or proprietary radio protocols.
For CDMA and other radio-link protocols, Internet protocol (IP) and other packets are fragmented into a number of radio frames that are transmitted over the wireless link. In the event of transmission errors, a frame is retransmitted up to a set number of times. If the frame is not successfully received by such retransmissions, the radio-link protocol aborts delivery of the frame, continues with the succeeding frames and leaves it to packet layer protocols to recover the lost data.